This invention relates to a method of manufacturing an elastic and flexible backing, which is intended to carry an electric conductor for heating seats or backs of chairs, cushions, mattresses and the like.
Electrically heated car seats, supports, cushions, rugs etc. are known. The electric conductor heating the object can consist of one or more electrically conductive wires and is applied in windings extending over the structural body of the carrier in question. Over this carrier and the conductor with its windings the covering and protecting outer layer of textile or other material, for example a compound of textile and foamed plastic, is laid. The conductor can also be applied directly on the backside of the outer layer.
All these known applications have in common that the conductor is applied in extended state on the carrying layer, i.e. the conductor between the bendings or windings is substantially non-resilient or "dead". This in its turn implies that the conductor is sensitive to fatigue and overload, which already after a short time gives rise to fractures. In a particular application, for example, electrically heated car seats, the conductor in such seats to-day has an average life corresponding to a covered distance of about 30 000 km. For solving this problem, the conductor has been enclosed in a plane strip, in which the conductor is permitted to form an S-like pattern. The object of this is that the strip takes up the tensile loads occurring and relieves the conductor, and at the same time a product is obtained which is easy to handle, simple to apply on the carrier or structural body. Because of the strip, the conductor cannot be laid out in rounded windings, but must be laid at sharp angles as it is turned through 180.degree. and overlapping. Its application, therefore, is time-consuming, and the double thickness of the strip in the folds forms undesirable local thickenings in the product.
The disadvantages of the electrically heated objects of the aforesaid type are eliminated by the present invention. Referring again to the car seat as an example, it can be mentioned that, according to the results of tests carried out, the car seat by the invention is given a life which exceeds substantially the life of an average car.